In recent years, efforts to reduce emissions of exhaust gases have substantially increased. The reason for these efforts is the strong rise in transportation means causing emissions. Therefore, it would be most efficient to develop new transportation means which have low emission levels and consume energy economically.
During a driving cycle, the exhaust emission of motor vehicles consist of two basic periods:
the cold-start period with high emission values and
a subsequent period with low emission values when the engine is warm.
The fact that the emissions of a vehicle driving on the road cannot be established on the roller-type test stand under specified conditions is a major problem. As a result, a test carried out on the roller-type test stand cannot be regarded as being totally complete, but rather as a partial examination. In addition to the tests on the test stand, the observance of emission standards for Ultra-Low-Emission-Vehicles (ULEV) as well as EURO III and IV will, therefore, be ascertained through the use of new in-situ control technologies.
In the USA, passenger cars may be equipped with an On-Board-Diagnosis (OBD) II-System which requires emission-related components to be monitored, such as lambda sensor, fuel system, secondary air system, exhaust gas circulation system, tank ventilation and the control of interruptions in combustion. However, the amounts of pollutants will not be measured. They are indirectly correlated with suitable sensor signals. German Patent 197 36 864.6: Vorrichtung zur Analyse des Abgases von Kraftfahrzeugen discloses a process for measuring emissions during driving. However, the amounts to be measured when the engine of the vehicle is warm are so low that measuring signals can hardly be detected in the natural noise.
For the three-way catalytic converter, there exists only one limit value of hydrocarbon (HC) whose observance is indirectly monitored through the ability of the catalytic converter to store oxygen. For this purpose, the measuring signals of two lambda sensors respectively located before and after the catalytic converter are compared and the signal ratio is correlated with the amount of hydrocarbons converted. This technique does not provide results on the actual HC emissions. For vehicles with ever-decreasing emission standards, however, direct measuring of emission quantities is more favorable.
In recent years, catalytic converter systems have been developed which fully reach their operating temperature within one minute. As a result, vehicle emissions are reduced to a minimum as opposed to the former situation where most of the pollutants were released during the cold-start period thus accounting for the greatest share of total emissions. In this case, after-burning, subsequent treatment or electric heating play an important role.
Furthermore, reduction systems have been developed in which an additional substance will be added to the exhaust flow to trigger a chemical reaction to achieve the desired change in the composition of the exhaust gases. Absorbent materials serve to retain pollutants during the cold-start period. The retained pollutants will be desorbed when the engine and the catalytic converter are warm. The adsorbent materials are used to retain unburned hydrocarbons based on activated carbons and to collect nitrogen oxides based on zeolite, for example. However, a process which makes it possible to reduce emission quantities in the exhaust gases not only during the cold-start period, but also in difficult situations as, for example, when defects occur in the combustion system or in the exhaust gas after-treatment system is needed.
In addition, the problem of how to make the emission measurement system suitable for use in airplanes, ships and diesel locomotives has not yet been dealt with.
This invention pertains to the emission control in motor vehicles but also in ships, airplanes and diesel locomotives. The control system may either be fitted into new vehicles by the manufacturer or be retrofitted by the driver in older vehicles. An adsorption system serves to reduce the vehicle emissions during the cold-start period, in case of malfunctions in the engine or in the exhaust gas after-treatment system and in times of high quantities of pollutants in the atmosphere. To regenerate the adsorbent masses, the pollutants will be desorbed, introduced into the combustion chamber and burned.